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nano > Prep, characterisation and structures of nano > Flashcards

Prep, characterisation and structures of nano Flashcards

1
Q

name 10 different types of synthesis

A 
hydrothermal
solvothermal
biomimetic
electrochemical
solvent-free
self-assembly
templating
dip-coating
exfoliation and cleavage
surface reaction controlled directional
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2
Q

what is hydrothermal synthesis

A

high temperature aqueous solutions at high vapour pressure to make a crystal

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3
Q

give examples of structures made by hydrothermal synthesis

A

H2Ti3O7 nanotubes

TiO2 + NaOH at 100C for 3 days - flat sheets rolled into layers using Na+ ions

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4
Q

what is solvothermal synthesis?

A

pressurised polar solvents at a temp above their bp

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5
Q

how does adding water affect a solvothermal synthesis

A

makes the single crystals hollow

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6
Q

how do you control size in solvothermal synthesis

A

via surface protection by organic molecules

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7
Q

give some examples of materials made by solvothermal synthesis

A

Nanotubes of perovskite
MOF-5
MnO3 crystallites on graphene

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8
Q

What is EEG? and give some properties

A

electrochemically exfoliated graphene
low level of defects, no O containing surface functional groups, mechanically strong, high conductivity, insoluble in water, soluble in DMF

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9
Q

What is GO? and give some properties

A

high level of defects, many OH groups, mechanically weak, low conductivity, soluble in water

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10
Q

what is biomimetic synthesis

A

application of biological principles for materials formation

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11
Q

give some examples of biomimetic synth

A

hydrothermal growth of ZnO twin-crystals with Gelatin or Gum Arabic
Calcite nanocrystals grown in alienate beads (controls size)

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12
Q

what compounds are made from electrochemical synthesis

A

anodic aluminium oxide (AAO)

anodic titanium oxide (ATO)

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13
Q

what is the ideal pore base shape according to the equifield strength model?

A

hemispherical

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14
Q

what is the main structural feature of compounds made by electrochemical synthesis

A

cylindrical pores

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15
Q

name a mechanism used in solvent-free synthesis

A

VLS - vapour-liquid-solid

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16
Q

what cal be made by VLS

A

Si nanowire

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17
Q

what controls the shape of a Si nanowire?

A

direction controlled by AAO holes, diameter controlled by size of gold

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18
Q

what compound is used for liquid coating to begin a Si nanowire?

A

SiH4

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19
Q

what is another example of a solvent -free synthesis?

A

catalytic growth by Co nanoparticles on Mg2SiO2 fibres

or Chemical Vapour Deposition eg carbon encapsulated Co nanoparticles

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20
Q

what is a benefit of chemical vapour deposition

A

low reaction temperature
low carbon concentration
short rxn time

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21
Q

what is the self-assembly phenomenon

A

then particles naturally form larger nanostructures

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22
Q

give 3 examples of self-assembly phenomenon

A

C60 nanowires
self assembly of surfactants used to template formation of mesoporous silicates
monolayer on a metal surface (alkanethiolate on Au(III) substrate)

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23
Q

give 3 examples of templating methods

A

porous single crystals - make porous structure (KIT-6) and fill with H2Cr2O7
AAO templated Si or Ni nanowire
electron beam induced metal nanowire growth - zeolite containing AgNO3 or CuCl irradiate with e beam giving ag or Cu nanowire.

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24
Q

what are the 5 stages of dip-coating?

A

1) immersion
2) start-up
3) deposition
4) drainage
5) evaporation of solvent

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25
Q

how do you control thickness of a layer in dip-coating?

A

depends on how fast substrate pulled out of coating liquid.

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26
Q

what are 3 things that can be made from exfoliation and cleavage methods?

A

graphene (top-down synthesis) -intercalation of ions followed by exfoliation of layer (by EtOH)
H2Ti3O7 nano sheet unrolled from a nanotube using ligands. nanotube made from crystal layers separated by Na+ ions
disassembly of 3D UTL framework into a 2D lamellae

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27
Q

what is the general shape of a structure formed by a surface reaction controlled by highly selective growth direction?

A

snowflakes

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28
Q

how to make a snowflake shaped Fe2O3 (hematite)

A

K3Fe(CH)6 + H2O –> (180C 20h) –> a-Fe2O3
1) nucleation
2)very slow hydrolysis of Fe(CN)6 3-
only grows along 110 directions

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29
Q

give some examples of how to control size and morphology.

A

nanoparticle by cleavage - thickness of layers and minimum lattice tension
Si wires by AAO - using nanotube template
Dip coating - thickness of liquid film
catalytic growth of Si nanowire - size of catalyst
Porous single crystals - Size of mesopores
C60 nanowires - thickness of solution film
surface protection - reaction rate.

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30
Q

what is braggs law?

A

n(lambda) = 2dsin(theta)

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31
Q

what determines peak position in XRD

A

function of d-spacings –> each peak accounts for a miller plane

32
Q

what determines peak intensities in XRD?

A

intensity proportional to |F|^2

33
Q

what determines peak width in XRD?

A

(width = FWHM - full width half height)

size of crystal - narrow peak = big crystal

34
Q

what are the 2 types of electrons picked up on by SEM

A

backscattered and secondary

35
Q

what does a secondary electron tell you in SEM?

A

morphology and type of material

36
Q

what info do backscattered electrons give in SEM?

A

number of backscattered electrons reaching the detector is proportional to the atomic number of the sample.

37
Q

what are ways of improving resolution of SEM + problems

A

a shorter wavelength of incoming energy gives higher res BUT a higher energy gives more damage to the sample
beam size
working distance

38
Q

what does TEM show?

A

direct structural images

39
Q

what are the 3 image formation mechanisms of TEM?

A

Mass-thickness contrast
Diffraction contrast
Phase contrast

40
Q

what is SAED?

A

selective area electron diffraction

41
Q

what do you need to do to reduce problems arising from spherical aberration

A

always want to under-focus the electron microscope to increase contrast

42
Q

how to increase mass-thickness contrast?

A

1) choose smaller objective aperture

2) use a lower accelerating voltage

43
Q

Explain EDX spectroscopy

A

outer shell electron jumps into inner shell hole and releases x-rays

44
Q

what is a big problem you have to take into consideration with EDX?

A

dead time - keep between 20-30% otherwise could give false elemental analysis

45
Q

What is the procedure for EDX?

A

use a reference sample with a similar composition to sample. Calculate K for alpha peaks then calculate the ratio for the solid solution. Do this 20-30 times and find avg value.

46
Q

what is a good sample material to use for EDX?

A

1) monobasic
2) similar composition
3) similar specimen thickness
4) >30 particles to find average for K

47
Q

what counts as a good peak for EDX?

A

high intensity, high energy no overlapping

48
Q

what is the main premise of STEM?

A

images formed by passing electrons through sufficiently thin specimen

49
Q

what is STEM good at?

A

detect transmitted or diffracted beam pixel-by-pixel
less beam damage due to small probe and short illumination time
z-contrast low for smaller atoms - cleans up messier structures

50
Q

What is the Cs correction?

A

dx = 0.66 Cs^1/4 (lambda)^3/4

51
Q

what is electron energy loss spectroscopy?

A

detects elements by core loss

useful for detecting light elements

52
Q

what is energy resolution of EELS cf EDX?

A

higher energy resolution (-1eV cf 10-90eV)

53
Q

what does EELS allow you to do?

A

detect chemical states, oxidation states and bonding of selected elements

54
Q

describe FIB

A

focussed ion beam - used to cut a sample
mill trenches, U-cut, attach to easy-lift probe, final cut and lift out sample, attach to TEM grid, free sample from probe, thin the sample and then run spec.

55
Q

what is AFM?

A

atomic force microscopy

for imagine, measuring and manipulating matter at the nanoscale.

56
Q

what is AFM based ?

A

Hooke’s law - F=-kx

forces between tip and sample surface deflecting a cantilever in contact and non-contact modes

57
Q

what is XPS?

A

x-ray photoelectron spectroscopy - eject photoelectrons from a sample and record spectrum.

58
Q

name some 0D nanomaterials

A

clusters, nano crystallites, core-shell nanoparticles, bimetallic alloys, nanoparticles of carbon

59
Q

name 2 methods of assembly of nanoparticles

A

1) reversed crystal growth

2) dipole field assembly

60
Q

what should a perfectly mixed alloy follow? + equation

A

Vegard’s law - a(A1-xBx)=(1-x)a(A)+a(B)

61
Q

what further effects can a point defect cause

A

local dislocation

62
Q

what defect has a crystal within the crystal?

A

domain structure

63
Q

what defect has 1 row shift in layers

A

anti-face defect

64
Q

what defect has two row shift in layers

A

twin defect

65
Q

what does the BFDH law say?

A

a crystal would rather grow faster up the way but slower to the sides

66
Q

properties of nanoclusters

A

very small - n>3; often fixed number of atoms; often no defined crystal structure

67
Q

examples of a nanocluster metal

A

Ru and Ag

68
Q

different 1D nanomaterials

A

carbon nanotubes, oxide nanotubes, C60 nanowire, Si nanowire, ZnO nano belts, Core-shell nanowires

69
Q

explain possible planar defects in Si nanowires

A

slower, thermodynamically controlled, growth goes in 111 direction with no defects
faster, kinetically controlled, growth goes in 112 direction with lots of defects

70
Q

give some examples of 2D nanomaterials

A

nano plates, graphene

71
Q

give some properties of graphene

A 
fast moving current
perfect thermal conductor 
1-atom thick planar sheet visible to eye
harder than diamond and 300 times harder than steel 
more reactive than graphite 
edge more reactive than surface
72
Q

what does adding Mn3O4 do to rGO

A

lowers conductivity
large amount of defects
uneven distribution of nanoparticles

73
Q

give some examples of 3D nanomaterials

A

mesoporous materials
ATO
inorganic frameworks
MOFs

74
Q

explain how a MOF is synthesised

A

MOF-5 - Zn5(OH)8(NO3)2.2H2O
microplanes grown to nanoplatelets, develop multiplayer particles to polycrystalline cubes inside the multilayer particles gives a polycryslltine cube.

75
Q

what is special about MOF synthesis

A

Reversed crystal growth mechanism

76
Q

what is important about O vacancies in Ce(1-x)Bi(x)O(2-d)

A

as number of oxygen vacancies increase, catalytic activity increases
there is an easy come easy go oxygen mechanism here.

nano (2 decks)

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